that Christie adapted this from a play somebody else wrote. I never knew she did that. Maybe this is how she learned her craft. Not a Christie fan, but some good things have been made from her works.
Reference is inscrutable because there is nothing to scrute.
This film was adapted from the 1936 play of the same name that was written by Agatha Christie and Frank Vosper.
That play was adapted from the 1934 short story Philomel Cottage which appeared in the Agatha Christie short story collection The Listerdale Mystery.
Source: The Bedside, Bathtub & Armchair Companion to Agatha Christie
The official Agatha Christie website says that Vosper alone wrote the play.
"My will is strong but my won't is weak"
The film 's credits say that the screenplay and dialogue were by Frances Marion, based on the play by Frank Vosper and a short story by Agatha Christie.
"My will is strong but my won't is weak"